looping through splines of a bezier circle, can only find 1 spline not 4
Your object has curve data. The curve data object holds a spline collection.

In each spline there are bezier_points or points.

You have mistaken a bezier point for a spline. The spline is a continued element made up from multiple points. As a curve data object can hold multiple splines (they can be discontinued/separate), it has a spline collection.

You can access the points with the Spline Info node. However if you want to produce a variable point list, I'd suggest inserting a script node which takes in a point list and outputs the modified point list.